The accurate weighing of an aircraft is generally effected during maintenance operations. Maintenance operations commonly take place in a hangar or in a closed installation, after the aircraft has been positioned on a chocking device. This chocking device includes in particular a set of chocks and there is a minimum distance (which can be equal to zero) that must be complied with between each of the chocks and a undercarriage leg of the aircraft.
The weight used for the operational distribution of an aircraft or for performance calculations is a combination of measurements, estimates and calculations on the basis of:                the operating empty weight (OEW) of the aircraft, obtained by averaging a sample of measurements for all the aircraft of a fleet,        the payload, based on estimates of the weight of the passengers and carry-on baggage and baggage in the hold together with the weight of the freight,        the fuel, the weight of which is measured in the fuel bowser and/or in the aircraft.        
The sum of the masses listed above enables an estimate to be obtained of the take-off weight (TOW). However, this estimated weight is not the real weight. This weight is used in the calculation of parameters of the aircraft. In particular, the center of gravity of the aircraft is calculated on the basis of this estimate.
The document FR 2 914 416 describes a system for determining the weight and the center of gravity of an aircraft in service at an airport. That system comprises weighing means embedded in the ground and disposed at a location the aircraft travels over, such as a taxiway leading to the runway. The aircraft is weighed when its undercarriage legs pass over the weighing means.
However, embedding the weighing means in the ground limits the use of the system to certain aircraft configurations.